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 A177861 Product of the quadratic nonresidues of prime(n). 2
 1, 2, 6, 90, 6720, 36960, 11642400, 283046400, 2412984420000, 1140422816332800, 1226781977195174400, 1863152400854384640000, 5988092802221559085056000, 112886540292742916603904000, 158983195607776600998537600000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) == (-1)^((p-1)/2) (mod p), if p = prime(n) is odd. REFERENCES Carl-Erik Froeberg, On sums and products of quadratic residues, BIT, Nord. Tidskr. Inf.-behandl. 11 (1971) 389-398. LINKS Rahul Gupta, Algorithmic Number Theory, Section 24.5 FORMULA a(n) = (p-1)!/A177860(n), where p = prime(n). EXAMPLE The quadratic nonresidues of prime(4) = 7 are 3, 5, and 6, so a(4) = 3*5*6 = 90. MATHEMATICA Table[ Apply[Times, Flatten[Position[ Table[JacobiSymbol[i, Prime[n]], {i, 1, Prime[n] - 1}], -1]]], {n, 1, 16}] CROSSREFS A125615 Sum of the quadratic nonresidues of prime(n), A177860 Product of the quadratic residues of prime(n), A177863 Product of the quadratic nonresidues of prime(n) modulo prime(n). Sequence in context: A179214 A128265 A087277 * A218151 A007188 A206156 Adjacent sequences:  A177858 A177859 A177860 * A177862 A177863 A177864 KEYWORD easy,nonn AUTHOR Jonathan Sondow, May 14 2010 STATUS approved

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Last modified August 20 22:45 EDT 2019. Contains 326155 sequences. (Running on oeis4.)